This invention relates to the assembling and packaging of integrated circuit devices and, more particularly, to provide a lead frame for such devices for stopping resin bleed and mold flash on Integrated Circuit lead finishes.
Integrated circuits in the form of semiconductor dies are first attached to a support pad of the lead frame. Contact or bond pads on the semiconductor device are then individually attached by wire bonding to corresponding contact pads on the ends of the leads.
After the wire bonding operation is completed, the lead frame is placed in a mold. The mold is provided from a reservoir with a quantity of insulating, molding compound. The molding compound is injected into the mold in order to encapsulate the circuit.
It is found useful by those skilled in the art to form the lead frames in a continuous strip. Each lead frame strip has an integrated circuit device attached to support pad as mentioned above. The support pads are themselves supported by two parallel siderails. Each siderail is located in the plane of the lead frame and on opposite sides of the die pad.
In the molding operation, mold cavities are formed around the lead frames to tightly close and seal upon themselves as well as the dam bar. The dam bar has a transverse portion that extends between pairs of adjoining leads. The dam bar restricts the flow of encapsulation material from the enclosed lead frame. After encapsulation, the dam bar and a portion of the mold flashing projecting between adjoining leads is removed by a punch. The punch is the typical metal punch that readily severs the metallic dam bar and also removes a portion of the projected mold flashing from between the leads of the lead frame.
During the molding operation, some excess resin can end up coating part of the lead. This resin could affect the formation of the lead's solder profile and electrical conductivity when soldering to the board. The excess resin is referred to as “resin-bleed”. The resin-bleed can appear as clear and called “clear-bleed” or as visible residue that often referred to as “mold-flash”. Chemical deflashing and media deflashing methods are commonly used in the industry to remove this excess resin on the leads.
As such, there has arisen a need for an improved lead frame for producing an encapsulated integrated circuit that has leads with limited mold flash or resin-bleed without the need for mold flash and resin-bleed removal.